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Grand Canyon is a sprightly young 6-million-year-old

IT’S just a spring chicken. The Grand Canyon in Arizona is almost 65 million years younger than we thought.

Back in 2012, work by Rebecca Flowers of the University of Colorado, Boulder, suggested that the canyon formed 70 million years ago, when dinosaurs still roamed. Now it seems the youngest part is just 5 or 6 million years old.

Karl Karlstrom of the University of New Mexico in Albuquerque and his colleagues used thermochronology to reveal when hot buried rocks first reached the surface and cooled. They took measurements at the base and rim in four sections of the canyon.

One section, Music Mountain, formed 50 to 70 million years ago – as Flowers found. But the rest was still buried then. “If you stand on what is now the rim of the youngest, eastern part of the Grand Canyon and look up you see just air,” says Karlstrom. “But 70 million years ago, you would have been covered by 2 kilometres of rock.”

The next section of the canyon formed 15 to 25 million years ago. But until the two outer sections made it to the surface 6 million years ago, the canyons were drained by different rivers. At that point, the Colorado river gouged a path along all four, creating the Grand Canyon (Nature Geoscience, doi.org/q7x). Karlstrom hopes his findings will resolve some of the uncertainty about the canyon’s age. “We are the first group to take all the data sets and show how we can reconcile them.”